Here is a solution by Rautavaara.
5/4 is indeed one of the most confusing meters to notate, and with missing the single-note of the full measure makes that meter really "painful".
Yet, this solution is somewhat original and not disturbing.

I think a better solution is the rhythm dot on both sides of the note (the dot to the left signifying half the value of the dot on the right), although that could be confusing in certain polyphonic situations.

I understand your distaste for tied notes to represent such a simple thing in 5/4, OCTO. It is too bad that the dot after a note has become so precise in its meaning and is no longer dependent on context as it was in the Baroque. Otherwise a dot could be used since there is no other possible meaning for a dotted whole note in 5/4. If some other symbol were used, I would prefer little unfilled circles to the crosses.

RMK and Schonbergian, I must admit that after a longer look, I agree that the idea is "somewhat original" but "a bit disturbing".

I had an excessive discussion at another forum a long time ago, with a person who wished to introduce a new notehead for the 5/4-whole note. The person had a huge intellectual capacity and a good knowledge and interest in notation, but what is strikingly important he didn't have experience in music performance, which is crucial in innovating new stuff.

Rautavaara OTOH, being a decent performer, only adds some "piccante" spices into his last notes...

Here is another solution of Crumb. Composers seem to suffer from this note-value.

There is undoubtedly a logic to that notation, but unfortunately the usual more complicated way of notating it is what musicians have become used to reading almost by instinct. Anything new has to be questioned and learnt, so it's probably best to keep to the standard notation (unless and until there is a widely accepted radical overhaul of almost all aspects of musical notation).

Here is another solution of Crumb. Composers seem to suffer from this note-value.

There is undoubtedly a logic to that notation, but unfortunately the usual more complicated way of notating it is what musicians have become used to reading almost by instinct. Anything new has to be questioned and learnt, so it's probably best to keep to the standard notation (unless and until there is a widely accepted radical overhaul of almost all aspects of musical notation).

I do agree with you, David.
The only moment when I find this note-value (in the standard notation) somehow awkward is when I need to notate a simple melody with ornaments, such as trill, which calls for trill extension, and the notation picture starts to be more complex than other note values (binary).